Create new SrcImplicit and SrcExplicit examples

[jchodera]

Something is wrong with these examples, since the hydrogens have sigma = 0. These examples no longer have their provenance information either, so they should just be regenerated.

[jchodera]

I've got a more general fix for this. Will open a PR.

[kyleabeauchamp]

I can also do this if desired, we can just copy in the data from the fah-projects repo:

https://github.com/choderalab/fah-projects/blob/master/src/equil_npt/equil_npt_final_step.pdb